1. Field of the Invention
The invention relates generally to the composition and structure of building materials. More specifically, the invention relates to re-enforced sheet piling segments.
2. Background Art
Sheet piling is a construction material that is commonly used to build walls such as retaining sea-walls. The sheet piling is typically manufactured in individual segments that are attached to other segments to form a continuous wall. Since the segments are usually driven into the ground for stability, the segments may be several meters tall.
Sheet piling was once commonly made with steel or other metals. However, such piling may now be made with fiber re-enforced polymers (FRP). FRPs are formed out of a cured resin that has been re-enforced with fibers made of materials such as glass. The resin typically may be polyester or vinylester. While not as strong as steel, these materials offer better performance due to resistance to corrosion and other effects of chemical environments. Steel is an example of an “isotropic” material in that loads are distributed equally through out the material. In contrast, FRPs are generally considered “anisotropic” in that loads are not distributed equally in the material. For example, a composite material such as fiberglass is stronger along the orientation of the glass fibers than in other areas of the material.
While the FRP materials are resistant to corrosion, they will absorb water when exposed to that environment for long periods of time. This is a particular problem when sheet piling made from FRPs is used to build a seawall. If the sheet piling is exposed long enough and absorbs enough water, the structure may become weakened to the point of failure. Additionally, when FRP sheet piling is used to build a seawall, it also is exposed to active pressure from soil on one side of the wall while being exposed to a passive pressure from the water on the other side. Over time, the panels of material can weaken and the panels may deform or fail catastrophically under this type of pressure alone or combined with any weakening of the material from water absorption.
The potential for such failures are particularly acute at the joints that join the panels together and at any corner or edge of a panel. According to modeling, maximum tension occurs at the corner angles of the panels. Typical solutions involved re-enforcing points of potential failure on a panel of sheet piling with a concave shaped re-enforcement. However, these re-enforcements have proven insufficient to provide the additional strength to a panel made of anisotropic materials (such as FRPs).